Stiffness enhanced tread element

ABSTRACT

A tire tread may be formed by simultaneously extruding a tread cap formed of a first material and a tread base formed of a second material having a substantially different stiffness property than the first material. One tread element may have a strip of the second material extending from the tread base into the tread cap and, a second tread element may also have a strip of the second material extending from the tread base into the tread cap.

I. BACKGROUND

A. Field of Invention

This invention generally relates to methods and apparatuses concerningpneumatic tires and more specifically to methods and apparatusesconcerning a pneumatic tire having a tread with strips of tread basematerial having a higher stiffness property that extend into the treadcap material having a lower stiffness property.

B. Description of the Related Art

It is known to those of skill in the art that the overall performance ofa pneumatic tire's tread pattern (including performance criteria such aswet handling, dry handling and stopping) may be compromised by thestiffness characteristics of the tread elements. Known methods ofincreasing the stiffness of a tread element include using relativelystiffer tread base materials and using relatively stiffer tread capmaterials. These methods typically have the disadvantage, however, ofcompromising other tread performance criteria.

It is also known, as taught in International Publication No. WO2005/063509, to provide a tire tread having sectors formed with a firstmaterial having a first modulus of elasticity and other sectors formedwith a second material having a second modulus of elasticity. A problemwith this method, however, is that the tire carcass must be movedsequentially from a first station where the first material is appliedand then to a second station where the second material is applied. Thismethod thus has disadvantages of increased complexity and increasedcost.

What is needed is a method of increasing the stiffness characteristicsof tire tread elements while minimizing the known disadvantages.

II. SUMMARY

According to one embodiment of this invention, a method of forming apneumatic radial tire may comprise the steps of: (A) providing a radialgreen tire carcass comprising a crown region and pair of sidewalls; (B)forming a green tire tread by simultaneously extruding a tread capformed of a first material and a tread base formed of a second materialhaving a substantially higher stiffness property than the firstmaterial; wherein step (B) comprises the step of: providing the greentire tread with: (1) a first portion having a first strip of the secondmaterial extending from the tread base into the tread cap; and, (2) asecond portion having a second strip of the second material extendingfrom the tread base into the tread cap; (C) applying the green tiretread to the crown region of the radial green tire carcass to form agreen tire; and, (D) vulcanizing the radial green tire to form apneumatic radial cured tire that comprises a tread having: (1) a firstshoulder tread element comprising the first strip extending from thetread base into the tread cap, wherein the first shoulder tread elementhas a stiffness property significantly different from the stiffnessproperty of the first shoulder tread element if the first shoulder treadelement was formed only of the first material; and, (2) a secondshoulder tread element comprising the second strip extending from thetread base into the tread cap, wherein the second shoulder tread elementhas a stiffness property significantly different from the stiffnessproperty of the second shoulder tread element if the second shouldertread element was formed only of the first material.

According to another embodiment of this invention, a tire may comprise:a carcass; and, a tread comprising: (1) a tread cap formed of a firstmaterial; (2) a tread base formed of a second material having asubstantially different stiffness property than the first material; (3)a first tread element having a first strip of the second material thatextends from the tread base through the tread cap to an outer groundcontacting surface of the tread; and (4) a second tread element having asecond strip of the second material that extends from the tread basethrough the tread cap to an outer ground contacting surface of thetread. The tread may be formed by simultaneously extruding the tread capand the tread base to include the first and second strips.

According to yet another embodiment of this invention, a tire maycomprise: a carcass; and, a tread comprising: (1) a tread cap formed ofa first material; (2) a tread base formed of a second material having asubstantially higher stiffness property than the first material; (3) afirst tread element having a first strip of the second material thatextends from the tread base into the tread cap; and (4) a second treadelement having a second strip of the second material that extends fromthe tread base into the tread cap. The tread may be formed bysimultaneously extruding the tread cap and the tread base to include thefirst and second strips. The first tread element may have a stiffnessproperty significantly greater than the stiffness property of the firsttread element if the first tread element was formed only of the firstmaterial and the second tread element may have a stiffness propertysignificantly greater than the stiffness property of the second treadelement if the second tread element was formed only of the firstmaterial.

One advantage of this invention is that different portions of a tiretread can be easily adjusted to have different stiffness properties.

Another advantage of this invention is that the tire tread can be easilyformed at a single station.

Other benefits and advantages of the invention will become apparent tothose skilled in the art to which it pertains upon a reading andunderstanding of the following detailed specification.

III. BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangement ofparts, embodiments of which will be described in detail in thisspecification and illustrated in the accompanying drawings which form apart hereof and wherein:

FIG. 1 is a cross-section of a first example tire constructed inaccordance with this invention.

FIG. 2 is a partial cross-section of a second example tire constructedin accordance with this invention.

FIG. 3 is a fragmentary front elevation of a tire tread splice bar witha first block with parts being broken away taken along the plane of line3-3 in FIG. 4 but also showing a second block also with parts beingbroken away.

FIG. 4 is a sectional view taken along the plane of line 4-4 in FIG. 3showing a conveyor for receiving the extruded tread.

FIG. 5 is a sectional view of the extruded tread taken along the planeof line 5-5 in FIG. 4.

FIG. 6 is an enlarged fragmentary plan view of the first block of FIG. 3taken along the plane of line 6-6 in FIG. 4 with parts being brokenaway.

FIG. 7 is a view similar to that shown in FIG. 1 but with the strips ofsecond material extending only into the tread cap, not through the treadcap.

IV. DEFINITIONS

“Apex” means a non-reinforced elastomer positioned radially above a beadcore.

“Axial” and “axially” mean lines or directions that are parallel to theaxis of rotation of the tire. “Axially inward” means lines or directionsthat are parallel to the axis of rotation of the tire and relativelytoward the inside of the tire. “Axially outward” means lines ordirections that are parallel to the axis of rotation of the tire andrelatively toward the outside of the tire.

“Bead” means that part of the tire comprising an annular tensile memberand shaped to fit the design rim.

“Carcass” means the tire structure apart from the belt structure, tread,undertread, and sidewall rubber, but including the beads and plies.

“Circumferential” means lines or directions extending along theperimeter of the surface of the annular tread perpendicular to the axialdirection.

“Cord” means one of the reinforcement strands of which the plies in thetire are comprised.

“Equatorial plane (EP)” means the plane perpendicular to the tire's axisof rotation and passing through the center of its tread.

“Footprint” means the contact patch or area of contact of the tire treadwith a flat surface at zero speed and under normal load and pressure.

“Ply” means a continuous layer of rubber-coated parallel cords.

“Radial” and “radially” mean directions radially toward or away from theaxis of rotation of the tire.

“Radial tire” means a belted or circumferentially-restricted pneumatictire in which the ply cords (which may or may not extend from bead tobead) are laid at cord angles between 65 degrees and 90 degrees withrespect to the equatorial plane of the tire.

“Tread” means an extruded rubber component which, when bonded to therest of the tire, includes that portion of the tire that comes intocontact with the road when the tire is normally inflated and undernormal load, that is, the footprint.

V. DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

Referring now to the drawings wherein the showings are for purposes ofillustrating embodiments of the invention only and not for purposes oflimiting the same, and wherein like reference numerals are understood torefer to like components, FIG. 1 shows a pneumatic tire 10 having atread 30 according to one embodiment of this invention. The tread 30 maybe positioned onto a carcass 12 of any conventional design. The carcass12 may include a pair of annular beads 14, 14 and a pair of apexes 16,16 positioned radially above the first and second annular beads 14, 14,respectively. The carcass 30 may also include one or more plies 18 thatmay extend from around the beads 14, 14, as shown. The carcass 30 maydefine a crown region 26 and a pair of sidewalls 28, 28. Otherconventional components may be positioned on the carcass 12 such as aninner liner 20, sidewall rubber portions 22, 22 and a belt package 24.Because a tire carcass and these other components are well known tothose of skill in the art, further details will not be provided here.

A tire tread 30 made according to one embodiment of this invention isshown in its green (uncured) state in FIG. 5 and in its cured state inFIG. 1. The tread 30 may have a tread cap 32 formed of a first material36 and a tread base 34 formed of a second material 38. The firstmaterial 36 may have a stiffness property (modulus of elasticity)substantially different than the second material 38. In one embodiment,the second material 38 has a substantially higher stiffness propertythan the first material 36. The second material may be extended into thefirst material sufficiently to significantly change the stiffnessproperty of the corresponding tread element (as compared to the treadelement if it was formed only of the first material). In one embodiment,shown in FIG. 7, the tread 30 may have a first portion 40 having a firststrip 44 of the second material 38 that extends from the tread base 34into the tread cap 32 and a second portion 42 having a second strip 48of the second material 38 that extends from the tread base 34 into thetread cap 32. In another embodiment, shown in FIGS. 1 and 5, the tread30 may have a first portion 40 having a first strip 44 of the secondmaterial 38 that extends from the tread base 34 through the tread cap 32to an outer ground contacting surface 46 of the tread 30 and a secondportion 42 having a second strip 48 of the second material 38 thatextends from the tread base 34 through the tread cap 32 to an outerground contacting surface 46 of the tread 30. While the locations forthe first and second strips 44, 48 on the tread 30 can be any chosenwith the sound judgment of a person of skill in the art, for theembodiment shown the first strip 44 is positioned in a first shoulder 50on the tread 30 and the second strip 48 is positioned in a secondshoulder 52. In this embodiment of the invention the first strip 44 isnot encompassed by any circumferential tread groove and the second strip48 is not encompassed by any circumferential tread groove. As is knownto those of skill in the art, the shoulders 50, 52 are good locations toadjust the tread stiffness so as to affect several tire performancecharacteristics. It should be noted that while the strips 44, 48 thatare described so far are positioned axially midway within tread elements54, 56 it is also contemplated to position the strips in tread elementsnearby tread grooves or to encompass tread grooves, such as shown withgrooves 58, 60 in FIG. 2. While the strips shown 44, 48 number only twoand are symmetrical with respect to the equatorial plane EP, it iscontemplated to use any number of strips that may, or may not, besymmetrical with respect to the equatorial plane EP.

A method of forming a tire tread 30 according to this invention may besomewhat similar to the method provided in U.S. Pat. No. 6,746,227titled Tire Tread Die which is commonly owned and which is incorporatedherein by reference. However, it should be noted that U.S. Pat. No.6,746,227 teaches only the use of very thin strips of conductivecompound to conduct static charge. FIGS. 3 and 4 show a tire tread die70 having a tread cap passage 72 and a tread base passage 74 incommunication with rubber extruders (not shown) that simultaneously feedor flow the first material 36 and the second material 38 into the treaddie 70 at extruder openings 76 and 78, respectively. In this way thetire carcass 12 does not have to be moved to various stations asrequired in the prior art. The tread cap passage 72 and the tread basepassage 74 may extend from spaced apart positions at an extruder side 80to a final die 82 having a final tread shaping opening 84.

With reference now to FIGS. 3-6, a first block 86 may be mounted in afirst area 94 of the tread cap passage 72 and may extend from an innersurface 88 of the tread cap passage 72 to surface 90 of the tread cappassage 72. A second block 92 may similarly be mounted in a second area96 of the tread cap passage 72 and may extend from an inner surface (notshown) of the tread cap passage 72 to a surface (not shown) of the treadcap passage 72. The first and second areas 94, 96 of the tread cappassage 72 may, in one embodiment, correspond to the first and secondshoulders 50, 52 on the tread 30. Each block 86, 92, may have a flowseparating protrusion such as a flow splitting tapered upstream edge 98for diverting the flow of the first material 36 around each block 86,92. Additional blocks can be added as required. Each block 86, 92 mayhave an opening 102 that extends from one end of the block to anopposite end. Communication of the tread base passage 74 with the blockopenings 42, 42 may be provided in any manner chosen with the soundjudgment of a person of skill in the art.

With reference now to FIGS. 1-6, in one embodiment, in order to form thefirst and second strips 44, 48 of the second material 38 (used to formthe tread base 34) into the first material 36 (used to form the treadcap 32), slots 104, 104 may be cut in downstream sides 106, 106 of theblocks 86, 92. The slots 104, 104 may extend between opposite ends ofeach block 86, 92, as shown. The diameter D of a block opening 102 andthe width W1 of the slot 104 may vary according to the tire performancedesired by the tire designer. In one embodiment, the width W1 of theslot 104 and the diameter D of the opening 102 are sized, depending onthe specific materials used to form the tread base 34 and tread cap 32,to produce strips 44, 48 to have a width W2 of at least 3 millimeters(mm) when the second material 38 is green (uncured), as shown in FIG. 5.In another embodiment, the strips 44, 48 have a width W2 of at least 5mm when the second material 38 is green. In yet another embodiment, thestrips 44, 48 have a width W2 of at least 3 mm when the second material38 is cured, as shown in FIG. 1. In another embodiment, the strips 44,48 have a width W2 of at least 5 mm when the second material 38 iscured. It is also contemplated to produce the first strip 44 to have awidth that is different from the width of the second strip 48.

As shown in FIG. 4, a conveyor 62 may be provided to convey the greentire tread 30, having an outer surface 46, to a suitable cutting stationwhere the tread is cut to length. The tread 30 may then be conveyed to atire building machine where it is applied to the crown region 26 of thecarcass 12 in a manner well known to those skilled in the art. Theassembled tire is then placed in a tire mold where it is vulcanized toform the cured tire 10, as shown in FIGS. 1 and 2. While the tread 30 ofthis invention can be applied to any style and size of tire chosen withthe sound judgment of a person of skill in the art, in one embodiment itis used with a pneumatic radial tire.

Stiffness property data was obtained as follows (according to RubberProcess Analyzer as RPA 2000™ instrument by Alpha Technologies at 100degrees Celsius and 1 Hertz) where kPa is kilopascal:

*cap material G′@10%: 250 to 3,000 kPa; preferred range: 500 to 2500 kPa

*base material: 1,000 to 8,000 kPa; preferred range 1,500 to 5,000 kPa

*delta stiffness difference: greater than 500 kPa; preferred greaterthan 1,000 kPa

Numerous embodiments have been described, hereinabove. It will beapparent to those skilled in the art that the above methods andapparatuses may incorporate changes and modifications without departingfrom the general scope of this invention. It is intended to include allsuch modifications and alterations in so far as they come within thescope of the appended claims or the equivalents thereof.

I claim:
 1. A tire comprising: a carcass; and, a tread comprising: (1) atread cap formed of a first material, wherein the tread cap includescircumferential tread grooves and extends from a first shoulder of thetire to a second shoulder of the tire, wherein the circumferential treadgrooves are encompassed within the tread cap; (2) a single tread baseformed of a second material having a stiffness of at least 500 kPa morethan the stiffness of the first material, wherein the tread base extendsfrom the first shoulder of the tire to the second shoulder of the tire;(3) a first tread element having a first strip of the second materialthat extends from the tread base through the tread cap to an outerground contacting surface of the tread, wherein the first tread elementis located on the first shoulder of the tire; and wherein the firststrip is not encompassed by any circumferential tread groove, andwherein the first strip is encompassed within the tread cap; (4) asecond tread element having a second strip of the second material thatextends from the tread base through the tread cap to an outer groundcontacting surface of the tread, wherein the second tread element islocated on the second shoulder of the tire; and, wherein the secondstrip is not encompassed by any circumferential tread groove, andwherein the second strip is encompassed within the tread cap; whereinthe second material has a stiffness of at least 1000 kPa more than thestiffness of the first material; wherein the second material has aG′@10% which is within the range of 1,500 kPa to 8,000 kPa as measuredat 100° C. and 1 Hz; wherein the only strips of the second materialwhich extend from the tread base through the tread cap to the outerground contacting surface of the tread are located on the first shoulderand the second shoulder of the tire; and wherein the tread is formed bysimultaneously extruding the tread cap and the tread base to include thefirst and second strips.
 2. The tire of claim 1 wherein: the tirefurther comprises a belt package positioned between the carcass and thetread; wherein the circumferential tread grooves are encompassedentirely within the tread cap; and, the tire is a pneumatic radial tire.3. The tire of claim 1 wherein the first and second strips have a widthof at least 3 millimeters.
 4. The tire of claim 1 wherein the first andsecond strips have a width of at least 5 millimeters.
 5. The tire ofclaim 1 wherein the first shoulder of the tire is located axially inwardfrom the most axially inward circumferential groove on the tread of thetire; and wherein the second shoulder of the tire is located axiallyoutward from the most axially outward circumferential groove on thetread of the tire.
 6. The tire of claim 5 wherein the first material hasa G′@10% which is within the range of 250 kPa to 3,000 kPa as measuredat 100° C. and 1 Hz.
 7. The tire of claim 5 wherein the second materialhas a G′@10% which is within the range of 2,000 kPa to 8,000 kPa asmeasured at 100° C. and 1 Hz.
 8. The tire of claim 5 wherein the firstmaterial has a G′@10% which is within the range of 500 kPa to 2,500 kPaas measured at 100° C. and 1 Hz.
 9. The tire of claim 5 wherein thesecond material has a G′@10% which is within the range of 1,500 kPa to5,000 kPa as measured at 100° C. and 1 Hz.
 10. The tire of claim 1wherein the first strip extends to the outer ground contacting surfaceof the tread through an area which is contained within the firstshoulder of the tire; and wherein the second strip extends to the outerground contacting surface of the tread through an area which iscontained within the second shoulder of the tire.